The present invention relates to a power-driven screwing tool.
A known screwing tool of this type (DE-PS 36 37 852) comprises a delayed-action clutch which acts to disengage a jaw clutch when the ceiling torque is exceeded, due to the pre-adjusted screwing depth, i.e. which then insures that a sufficient clearance exists between the end faces of the oppositely arranged jaws of the two clutch elements forming the jaw clutch. The reason why such separation must be ensured lies in the fact that in the case of a screwing tool with depth stop the drive shaft of the screw driver moves in axially forward direction relative to the tool, which is fixed to the depth stop, whereby it causes the jaw clutch to get disengaged, if only gradually, by entraining the one clutch element of the jaw clutch, while there remains a tendency, at the point of transition for disengagement, to maintain the engagement when the screwing tool is further loaded, which causes the jaws of the jaw clutch to rip past each other or to hit against each other causing considerable noise. This is not only disturbing, but may also lead to considerable wear in the area of the jaw clutch which is responsible for separating the drive shaft from the electric drive motor. As a consequence of these phenomena, vibrations may occur and heat may develop.
In order to remedy this problem, an arrangement has been proposed (DE-PS 35 10 605) in which a spring-loaded intermediate disc likewise provided with jaws is arranged between the two halves of the jaw clutch of a screwing tool, which intermediate disc is mounted to rotate freely and to move in axial direction along the drive shaft of the tool. The connection between the end faces of this intermediate disc and the adjoining clutch elements, which exhibit corresponding complementary shapes, is ensured by cams on the one side and by claws on the other side, the claws being provided on one side with inclined surfaces for axial lift-off, so that the intermediate disc is also permitted to move in the axial direction. This then enables these clutch elements to be separated fully, supported by the action of a spring, at the very moment when the ceiling torque is reached or, to say it in other words, at the very moment when the drive shaft, which can be displaced in the axial direction, has been moved outwardly to a point where the cams in one clutch area are no longer capable of transmitting a torque because they are coming out of engagement, because on the other side of the intermediate disc the claws come to slide off the inclined surfaces at the same moment, whereby the axial clearance in the cam transmission area of the clutch is enlarged additionally.
However, it is a problem encountered in connection with this solution that the additional arrangement of the intermediate disc requires additional space and makes the structure as a whole more complex. In particular, this intermediate disc, which is freely movable in both the axial and radial directions, constitutes an element subject to wear which, therefore, may increase the susceptibility to trouble of the whole unit.
The power-driven screwing tool described by the beforementioned publication (DE-PS 36 37 852) seeks to overcome this problem by doing without any such intermediate clutch element, i.e. the additional intermediate disc, and by designing the transition area between the clutch element of the jaw clutch on the drive-shaft end and the drive shaft in a particular way so as to form a delayed-action clutch. This delayed-action clutch allows a relative rotary movement between the drive shaft and this clutch element only over a small angle. It is implemented by an arrangement in which a transverse pin fixed against rotation on the drive shaft engages closed bores or inclined transverse guides arranged on the clutch element. These inclined stop faces ensure at the same time that during movement of the transverse pin along its guides, an axial relative displacement occurs between the clutch element and the drive shaft which, upon disengagement of the clutch of the unit when the desired screwing depth has been reached, ensures in the conventional manner that the disengagement of the jaw clutch occurring when the transmitted torque starts to disappear--when the ceiling torque is reached--is completed by an enlargement of the existing clearance. However, it is a problem of this known solution that on the one hand guides are to be worked into the clutch element of the jaw clutch on the drive-shaft end, which guides have the form of closed cavities and require in addition the corresponding inclined surfaces, which can be realized only with great difficulty, and that in addition the assembly of the components is also rendered much more difficult.
Now, it is the object of the present invention to introduce considerable simplifications in the area of the delayed-action clutch of such a power-driven screwing tool, while maintaining on the other hand the rapid disconnecting processes provoked by the inclined surfaces at the transition point, when the ceiling torque is reached.